The Collaborative International Dictionary of English v.0.48:

Costate \Cos"tate\ (k?s"t?t), Costated \Cos"ta*ted\ (-t?-t?d),
   a. [L. costatus, fr. costa rib.]
   Having ribs, or the appearance of ribs; (Bot.) having one or
   more longitudinal ribs.
   [1913 Webster]